Apparatus for agglomerating and/or drying and sterilizing particulate material

ABSTRACT

Apparatus for agglomerating and/or drying and sterilizing particulate material, comprising a vibratory conveyor arranged to convey the particulate material between two electrodes of a radio frequency treatment device capable of heating the moisture contained by the particles while the particles are being agitated in such fashion that they are only in transient contact with parts of the apparatus and with each other as they are treated. The apparatus is particularly useful for treating particulate materials, such as dehydrated citrus juice and gunpowder, which are specially sensitive to heat.

United States Patent [191 Sargeant 1 APPARATUS FOR AGGLOMERATING AND/OR DRYING AND STERILIZING PARTICULATE MATERIAL [76] Inventor: Ralph G. Sargeant, 408 W. Windsor St., Lakeland, Fla. 33803 22 Filed: Apr. 18, 1974 21 Appl. No.: 461,963

[52] US. Cl. 219/10.8l; 198/220 BA; 209/127 B;

219/1069 [51] Int. Cl. HOSb 9/04 Field of Search 219/1081, 10.69, 10.73,

219110.71, 10.55 A; 209/127 B, 127 A, 127 C; 198/220 BA, 220 DC [56] References Cited UNITED STATES PATENTS 1,355,477 10/1920 Howell 209/127 C 2,031,086 2/1936 Woodruff et a1. 198/220 VACUUM P/ PU M P RF GENERATOR May 20, 1975 7/1949 Castellan 219/1081 X 11/1970 Ingram 219/1081 X Primary ExaminerBruce A. Reynolds Attorney, Agent, or FirmRoylance, Abrams, Berdo & Kaul [57] ABSTRACT Apparatus for agglomerating and/or drying and sterilizing particulate material, comprising a vibratory conveyor arranged to convey the particulate material between two electrodes of a radio frequency treatment device capable of heating the moisture contained by the particles while the particles are being agitated in such fashion that they are only in transient contact with parts of the apparatus and with each other as they are treated. The apparatus is particularly useful for treating particulate materials, such as dehydrated citrus juice and gunpowder, which are specially sensi tive to heat.

10 Claims, 5 Drawing Figures PART ICULATE MATERIAL wgmgg 1%(201975 3.8851 19 SHEET aor 2 APPARATUS FOR AGGLOMERATING AND/OR DRYING AND STERILIZING PARTICULATE MATERIAL RELATED APPLICATIONS Apparatus according to the invention are useful in practicing the method disclosed and claimed in my copending application Ser. No. 461,964, filed concurrently herewith. My copending application Ser. No. 461,962, filed concurrently herewith, discloses and claims a related method for sterilizing particulate solids.

BACKGROUND OF THE INVENTION Particulate materials of various kinds are commonly subjected to thermal treatment, as in drying, or to treatments in which heat is necessarily employed as part of a more extensive treatment. as in agglomeration. For many particulate materials. conventional thermal treatments, as by steam or by hot gas, are acceptable. Other more sensitive materials, however, frequently cannot tolerate conventional heat treatment without deleterious effects. Typical of such materials are the dehydrated citrus juices in powder form, smokeless gunpowder, and the like.

Additionally, it has been desirable to agglomerate finely particulated materials, such as dehydrated juices in powder form, which heretofore have been virtually impossible to agglomerate regardless of the problem of heat sensitivity. It has also been desirable to minimize or destroy any microbiological population which may be present in particulate materials, without requiring rigorous thermal or chemical treatments of the particles, but no apparatus capable of accomplishing that end has heretofore been available.

OBJECTS OF THE INVENTION It is accordingly a general object of the invention to devise an apparatus capable of carrying out such treatments as agglomeration, drying and sterilizing of finely particulate solid materials without adversely affecting the particulate material.

Another object is to provide an improved apparatus for agglomerating particulate solids, with the apparatus being especially useful for agglomerating those materials which are sensitive to heat or to which it is not desirable to add moisture.

A further object is to provide an apparatus for subjecting finely particulate solid materials to a radio frequency field in such fashion that the moisture content of each particle is uniformly heated dielectrically, with the dielectric heating also being uniform throughout the entire mass of particles being treated.

SUMMARY OF THE INVENTION Broadly considered, apparatus according to the invention comprise a vibratory conveyor capable of both conveying particulate solid material and causing the particles to move in directions generally transverse to the line of conveyor feed so that the mass of particles being conveyed is continuously agitated to provide only transitory, essentially instantaneous contact of the particles with the involved surfaces of the conveyor, the conveyor being arranged to pass the particulate mate rial between two elongated, spaced electrodes con nected to a radio frequency generator. Advanta geously, the surfaces contacted by the particles are of non-metallic material of such dielectric property as to avoid undue dielectric heating of the parts presenting those surfaces, and one or both of the electrodes are cooled to prevent heat build-up.

In order that the manner in which the foregoing and other objects are achieved according to the invention can be understood in detail, particularly advantageous embodiments thereof will be described with reference to the accompanying drawings, which form part of the original disclosure hereof, and wherein:

FIG. 1 is a semi-diagrammatic side elevational view of a treatment system employing one apparatus according to the invention;

FIG. 2 is a longitudinal vertical sectional view of the apparatus of FIG. 1;

FIGS. 3 and 4 are transverse sectional views taken generally on lines 3-3 and 4-4, FIG. 2, respectively; and

FIG. 5 is a transverse sectional view illustrating a portion of the apparatus according to another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION Referring first to FIG. 1, the system comprises an elongated generally horizontal trough I of U-shaped transverse cross-section. The material to be treated is supplied to one end of trough 1 via a feeding funnel 2. T ough l is vibrated by a conventional electromagnetic vibrator 3, with the vibration being essentially reciprocatory along a line, such as line 4, which slants upwardly and toward the end of the trough opposite fun nel 2. With the trough vibrated at, e.g., 750-2,000 cycles per second, particulate material supplied to the trough I by funnel 2 is both agitated and caused to transverse the trough lengthwise, ultimately being discharged therefrom at the end opposite the funnel. The nature of the agitation caused by vibration of the trough is such that the particles supplied via funnel 2 are in motion, through the atmosphere in which the trough is located, for most of the time required to pass through the trough, contact of the particles with the trough being essentially instantaneous, and extensive random particle-to-particle contact accordingly occurs.

Radio frequency energy is applied for a major portion of the path of travel for the particulate material being treated. Thus, a conventional RF generator 5 is connected to electrodes 7 and 8, electrode 7 being spaced above the bottom wall of trough l and extending lengthwise of the trough and parallel to the bottom wall, and electrode 8 being located immediately below the bottom wall of the trough and extending parallel to both the trough and electrode 7. RF generator 5 is constructed to provide radio frequency energy at a frequency in the range of 570 mhz., the generator operating typically at an RF voltage of l0,000-27,000 and a plate current of l.53 amp. Trough l is advantageously formed of polymeric material having good di electric properties, i.e., a low dielectric constant and a low power factor, so as not to be significantly heated by the radio frequency energy. Electrodes 7 and 8 are typically of aluminum, and lower electrode 8 is advantageously a hollow, liquid-cooled electrode, with the coolant, such as a machine oil which is not a conductor for radio frequency energy, supplied via input conduit 9 and outlet conduit 10, the oil being maintained at a suitable relatively low temperature by being passed through a conventional heat exchanger {not shown). The combination of trough l, vibrator 3 and electrodes 7,8 is enclosed in a suitable radio frequency shielding structure 11 which can be of aluminum sheet. An adjustable levelling blade 12 is provided to determine the depth of the bed of particulate material on the bottom of trough l.

The treated material is delivered via a funnel 13 to a conduit 14 communicating with a chamber l at a lateral point near the top of the chamber. Chamber 14 has a bottom opening to which a vertically depending discharge conduit I6 is connected, passage of material through conduit 16 being controlled by a valve 17. Within chamber 15, a partition 18 slants downwardly toward discharge conduit 16, the partition being spaced from the discharge opening of conduit 14 by a distance greater than its spacing from the location of discharge conduit 16. The bottom edge of partition 18 is spaced slightly above the bottom wall of chamber 15. At its top, in a location on the side of partition 18 opposite conduit 14, chamber is provided with an open ing communicating with a conduit 19 connected to a vacuum pump P. With the vacuum pump operating continuously, a current of atmospheric air is drawn through conduit 14 into chamber 15, and the agglomer ated material discharged from trough l is entrained in that air current. When the agglomerated material enters chamber 15, the solid material impinges on partition 18 and descends by gravity into discharge conduit 16.

The embodiment of the apparatus shown in FIGS. 2-4 comprises a generally horizontal trough 20, a conventional electromagnetic vibrator 21, an upper electrode 22, and a lower electrode 23.

Trough 20 consists of an elongated integral body formed of polymeric material having good dielectric properties so as not to be heated by radio frequency energy. Typically, the trough can be of polytetraflw oroethylene, or of a fiber glass reinforced epoxy resin, or a fiber glass reinforced silicone polymer. The trough is of Ushaped transverse cross section, having a flat bottom wall 24 and flat side walls 25,26, and can be open at both ends. Trough 20 can be supported in hori zontal position solely via its connection to vibrator 21, or additional supporting means (not shown) of the vi bration isolator type can be employed.

Vibrator 21, FIG. 2, is stationarily mounted and includes a vibratory output member 27. A rigid channel member 28 extends along the bottom face of bottom wall 24 of the trough, being aligned along the longitudinal center line of the trough and rigidly secured to bot tom wall 24, as by fasteners 29 made of polymeric material. The output member 27 of vibrator 21 is secured to the bottom face of a block 30 which is disposed in and rigidly secured to one end portion of channel member 28. Block 30 can be of rigid dielectric material to provide additional RF isolation for the vibrator.

Electrodes 22 and 23 are elongated hollow metal electrodes of rectangular plan conforming to that of the trough. Advantageously, the electrodes are of aluminum. Electrode 22 comprises a body 31 having a flat rectangular bottom wall 32, flat side walls 33 and 34, and flat end walls 35 and 36, the top of the hollow structure defined by body 31 being closed by a flat top plate 37. A plurality of partitions 38 project inwardly from wall 33, and a plurality of partitions 39 extend in wardly from wall 34, the partitions being shorter than the space between the side walls. Partitions 38 are spaced apart lengthwise of the electrode, as are partitions 39, and the two sets of partitions alternate so that one partition 38 is located between each adjacent pair of the partitions 39, and the partitions and the electrode walls thus cooperate to define a tortuous flow path from end wall 35 to end wall 36. A cooling water supply tube 40 opens through end wall 35 to supply water to the interior of the electrode. and the cooling water is discharged via an exhaust tube which opens through end wall 36.

Electrode 23 similarly comprises a main body 40 having a flat rectangular bottom wall 41, flat side walls 42 and 43, and flat end walls 44 and 45, the top of the hollow structure defined by body 40 being closed by a top member 46 which is mainly flat but includes a longitudinally extending central channel 47 dimensioned to freely accommodate member 28. Alternating partitions 48,49 are provided as described with reference to partitions 38,39. Cooling liquid, such as a suitable machine oil, is supplied to the interior of electrode 23 by a supply tube 50 at end wall 44 and is discharged via exhaust tube 51 at end wall 45. Electrodes 22 and 23 are connected to a radio frequency generator (not shown) having the characteristics and in the manner hereinbefore described with reference to FIG. 1.

Adjacent each end of electrode 22, top plate 37 has two transversely aligned laterally projecting mounting ears 55. Similarly, top plate 46 of electrode 23 has, at each end of the electrode, a pair of mounting cars 56. At each end of the pair of electrodes, two vertical threaded mounting rods 57, FIG. 3, of polytetrafluoroethylene or like dielectric, are provided, each rod 57 extending through openings in the corresponding pair of ears 55,56. The headed lower ends of rods 57 are engaged below ears 56, and nuts 58 secure plates 37,46 rigidly to the rods 57. The upper ends of rods 57 are secured to suitable mounting members 59 by nuts 60, FIG. 2.

The electrodes are connected to a conventional RF generator by a conventional coaxial cable 6], a conventional coaxial connector 62 serving to connect the central conductor 63 electrically to plate 37, the shell of the connector 62 being connected to outer conductor 64 and, by a conductor not shown, to plate 46.

Electrodes 22 and 23 are of equal length and are mutually parallel and in vertical alignment. Trough 20 is longer than electrodes 22,23 and is disposed between the two electrodes, with the input end 200 of the trough projecting well beyond the respective vertically aligned ends of the electrodes. A delivery funnel 65 is arranged above the delivery end 20a of the trough, being supported by any suitable support means, such as the shielding means for the apparatus (not shown), independent of the trough. As seen by comparison of FlGS. 2 and 4, the spout 66 of the funnel is of elongated reet angular cross section, the width of the spout being only slightly less than the space between side walls 25,26 of trough 20, and the funnel being so positioned that the open bottom end of spout 66 is spaced above bottom wall 24 of the trough by a distance slightly greater than the depth desired for the bed of particulate material to be established in the trough.

Between funnel 65 and electrodes 22 and 23, an ad justable blade 67 is provided to assure that the depth of the bed of particulate material will be essentially uniform across the width of the trough. Blade 67 is in the form of a flat plate of polytetrafluoroethylene or equivalent dielectric material, the plate being slotted near its ends to accommodate side walls 25.26 of the trough in slidable fashion so that, with the blade lying in a vertical plane, it can be moved upwardly or downwardly to adjust the distance between the bottom edge 67a of the blade and bottom wall 24 of the trough. A projection 68 is secured to blade 67 at the top thereof and projects toward the electrodes. A vertical adjusting screw 69 has an unthreaded shank portion journalled in projection 68, the threaded shank of the screw depending therefrom and being engaged in a threaded bore through a cross member 70, the ends of the cross member being rigidly fixed to side walls 25 and 26, respec tively. Knurled head 71 of the screw 69 is exposed above support 68 so that manual manipulation of the screw to adjust the vertical position of blade 67 is easily accomplished. Elements 68-71 are advantageously of rigid polymeric material having good dielectric characteristics so as not to be unduly heated by radio frequency energy.

Vibrator 2] acts through rigid output member 27 and channel member 28 to vibrate trough at relatively high frequency and low amplitude in the direction of arrow 21a. During each cycle of vibratory movement, the trough is moved through a very short distance up' wardly and away from vibrator 21 and then in the reverse direction, downwardly and toward the vibrator. By design and adjustment of the vibrator 21, the frequency and amplitude of the vibratory movement of the trough can be predetermined in accordance with the particle size and density of the particulate material involved, and the throughput rate (and thus the resi dence time) required for the particular thermal treatment to be accomplished. Advantageously, the trough is vibrated at a frequency of 750-1000 cycles per second, with an amplitude or excursion of, e.g., less than one-sixteenth inch.

The particulate solid material is supplied at a constant rate such as to establish on the bottom wall of trough 20 a bed of particulate material having a static depth, i.e., that depth which would exist if the trough were not vibrating, typically on the order of onesixteenth inch, the bed being rendered uniform by the levelling action of blade 67. The vibratory motion imparted to the trough by vibrator 21 serves two functions, which can be considered broadly as conveying and agitating. Conveying occurs because the upward portion of each cycle of vibratory motion of bottom wall 24 of the trough projects all of the particles upwardly and toward the delivery end of the trough, the particles then being out of engagement with the bottom wall until the upward portion of the next cycle of move ment. Thus, considering the idealized case of only a single particle, rather than a bed of particles, the single particle is engaged and projected by a different point on the surface of the bottom wall during each cycle of the vibratory movement, the points being spaced apart by small distances so as to lie in a series progressing from the input end to the discharge end of the trough. The agitating effect has two advantageous characteristics. First, since contact between the particles and bottom wall 24 of the trough is instantaneous, the particles are kept in essentially constant movement and, as a re sult of that movement, the surfaces of the particles are subjected to the air or other gaseous atmosphere in which the trough is located rather than being in long term contact with the solid surfaces of the trough or the surfaces of adjacent particles. Next, since the static depth of the bed of particles is large in comparison to the particle size, frequent particle-to-particle contact, random in nature, occurs. Additionally, with side walls 25, 26 of the trough having a height which is large in comparison with the bed thickness and the amplitude of vibratory movement, trough 20 serves to confine the particulate material to a path of travel which is between and aligned longitudinally with the elongated electrodes 22 and 23.

A particular advantage of the apparatus is that it makes it possible to pass a mass of particulate material through a defined treating zone and to subject the material to radio frequency energy throughout its residence time in the treating zone, with each particle (or each particle and each agglomerate, in the case of agglomeration) being subject to only a minimum of contact with other surfaces during the treatment. In the case of thermal drying or drying and sterilization, for example, a more predictable and assured treatment is accomplished than has heretofore been possible with apparatus in which the particulate material is supported as a static bed.

The embodiment of FIGS. 2-4 has the advantage that the surfaces of the trough are of inert material, so that, for example, particulate materials which cannot safely be passed in contact with metal can be treated. Thus, the embodiment of FIGS. 2-4 can be employed to dry smokeless powder. This embodiment also has the distinct advantage that the thermal input to the particulate material being treated is essentially limited to the heat arising from dielectric heating of the free moisture contained by the particles, both electrodes 22 and 23 being water-cooled.

Alternatively, the trough 20 and lower electrode 23 can be replaced by the combined trough and electrode shown in FIG. 5. Here, the trough comprises two spaced, parallel side members 125, 126 formed of polytetrafluoroethylene or the like, the side members having an outwardly projecting base flange a, 1260, respectively, and being secured by nylon screws I29 to a flat metal plate 123 which constitutes the lower electrode of the apparatus. The combined trough and electrode 120 can be secured directly to the rigid channel member 28, FIG. 2, and additionally supported by conventional vibration isolator means (not shown), the support rods 57, FIGS. 2 and 3, serving only to support the upper electrode 22. In the embodiment of FIG. 5, lower electrode 123 is not specially cooled.

What is claimed is:

1. In an apparatus for accomplishing thermal treatment, as in agglomerating, drying and sterilizing, of particulate solid materials having a significant moisture content, the combination of two elongated electrodes of substantial width arranged one above the other and spaced apart by a significant distance to define a treating zone;

at least one of said electrodes being hollow and equipped with inlet and outlet means for the flow of a cooling liquid therethrough;

means for operatively connecting the electrodes to a radio frequency generator;

conveyor means extending between said electrodes and through said treating zone in a direction lengthwise of the electrodes,

said conveyor means having a supporting surface which has an input end and a discharge end and is at least substantially as long and wide as the electrodes and is capable of receiving and supporting a relatively thin bed of the particulate material, said conveyor means comprising vibrating means connected to vibrate said surface to both agitate the particulate material and cause the particulate material to move from the input end to the discharge end of said supporting surface, there being a substantial free space between said supporting surface and the upper one of said two electrodes, which space can be occupied by a gaseous atmosphere of predetermined temperature and humidity, said vibrating means being constructed and arranged to impart to said surface vibratory motion having components directed respectively toward and away from said upper electrode; and means for supplying particulate material to the input end of said supporting surface. 2. The combination defined in claim 1, wherein said conveyor means comprises an elongated trough and said supporting surface is the upper surface of said trough. 3. The combination defined in claim 2, wherein said trough is longer than said electrodes and said input end projects beyond the adjacent end of said upper electrode.

4. The combination defined in claim 2, wherein said trough is of inert, non metallic material having a low dielectric constant and low power factor.

5. The combination defined in claim 4, wherein the lower one of said electrodes is separate from said trough, and

the combination further comprises a plurality of upright members rigidly interconnecting said electrodes and by which the combination of said electrodes can be connected to a support, said upright members being of a material having a low dielectric constant and a low power factor. 6. The combination defined in claim 4, wherein the lower one of said electrodes is separate from said trough. and both of said electrodes are hollow structures each equipped with inlet and outlet means for the flow of cooling liquid therethrough. 7. The combination defined in claim 6, wherein said conveyor means comprises an elongated rigid member extending along and rigidly secured to the lower face of the bottom wall of said trough; said lower electrode comprises an upper wall member formed with an elongated channel through which said elongated rigid member extends; and said vibrating means is connected to said elongated rigid member. 8. The combination defined in claim 2, wherein said vibrating means is connected to said trough and oriented to impart thereto generally reciprocatory motion along a line slanting upwardly and toward the discharge end of the trough. 9. The combination defined in claim 2, wherein said upper electrode is hollow. and the lower one of said electrodes comprises a metal plate constituting the bottom wall of said trough. 10. The combination defined in claim 2, wherein said trough comprises a flat metal plate constituting the bottom wall of the trough. and side wall members secured to said plate and projecting upwardly therefrom, said side wall members being of a material having a low dielectric constant and a low power factor. said plate constituting the lower one of said electrodes. 

1. In an apparatus for accomplishing thermal treatment, as in agglomerating, drying and sterilizing, of particulate solid materials having a significant moisture content, the combination of two elongated electrodes of substantial width arranged one above the other and spaced apart by a significant distance to define a treating zone; at least one of said electrodes being hollow and equipped with inlet and outlet means for the flow of a cooling liquid therethrough; means for operatively connecting the electrodes to a radio frequency generator; conveyor means extending between said electrodes and through said treating zone in a direction lengthwise of the electrodes, said conveyor means having a supporting surface which has an input end and a discharge end and is at least substantially as long and wide as the electrodes and is capable of receiving and supporting a relatively thin bed of the particulate material, said conveyor means comprising vibrating means connected to vibrate said surface to both agitate the particulate material and cause the particulate material to move from the input end to the discharge end of said supporting surface, there being a substantial free space between said supporting surface and the upper one of said two electrodes, which space can be occupied by a gaseous atmosphere of predetermined temperature and humidity, said vibrating means being constructed and arranged to impart to said surface vibratory motion having components directed respectively toward and away from said upper electrode; and means for supplying particulate material to the input end of said supporting surface.
 2. The combination defined in claim 1, wherein said conveyor means comprises an elongated trough and said supporting surface is the upper surface of said trough.
 3. The combination defined in claim 2, wherein said trough is longer than said electrodes and said input end projects beyond the adjacent end of said upper electrode.
 4. The combination defined in claim 2, wherein said trough is of inert, non-metallic material having a low dielectric constant and low power factor.
 5. The combination defined in claim 4, wherein the lower one of said electrodes is separate from said trough, and the combination further comprises a plurality of upright members rigidly interconnecting said electrodes and by which the combination of said electrodes can be connected to a support, said upright members being of a material having a low dielectric constant and a low power factor.
 6. The combination defined in claim 4, wherein the lower one of said electrodes is separate from said trough, and both of said electrodes are hollow structures each equipped with inlet and outlet means for the flow of cooling liquid therethrough.
 7. The combination defined in claim 6, wherein said conveyor means comprises an elongated rigid member extending along and rigidly secured to the lower face of the bottom wall of said trough; said lower electrode comprises an upper wall member formed with an elongated channel through which said elongated rigid member extends; and said vibrating means is connected to said elongated rigid member.
 8. The combination defined in claim 2, wherein said vibrating means is connected to said trough and oriented to impart thereto generally reciprocatory motion along a line slanting upwardly and toward the discharge end of the trough.
 9. The combination defined in claim 2, wherein said upper electrode is hollow, and the lower one of said electrodes comprises a metal plate constituting the bottom wall of said trough.
 10. The combination defined in claim 2, wherein said trough comprises a flat metal plate constituting the bottom wall of the trough, and side wall members secured to said plate and projecting upwardly therefrom, said side wall members being of a material having a low dielectric constant and a low power factor; said plate constituting the lower one of said electrodes. 